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Plant Respiration

Middle schoolBiologyOxygen-limited virtual seed respirometry with isothermal ideal-gas pressure and a diagnostic manometer

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About this experiment

Measure the respiration of a sealed seed sample by following oxygen consumption, carbon dioxide production and the resulting pressure signal. Compare the same sample with and without carbon dioxide absorption.

Learning goals

  • Connect gas consumption to a measurable pressure change.
  • Explain why removing respiratory carbon dioxide changes a respirometer signal.
  • Compare temperature and oxygen supply without confusing rate with total available oxygen.

How to use it

  1. 1Run the seed chamber for six hours and record oxygen consumption and manometer height.
  2. 2Disable carbon dioxide absorption at respiratory quotient one and repeat the trial.
  3. 3Compare two temperatures with the same mass and initial oxygen supply.
  4. 4Set the oxygen percentage to zero and check the predicted aerobic respiration.

The model

A fixed-temperature pressure change measures net gas loss, not oxygen alone.
The diagnostic water manometer converts pressure to a signed height difference.

Assumptions

  • The chamber is rigid, sealed and isothermal at the selected trial temperature. The selected initial pressure is always 101325 Pa. Gas amounts are volume equivalents at those initial conditions.
  • The illustrative oxygen-use rate has a Q10 of 2, scales with seed mass and saturates with oxygen. It is not calibrated to a particular plant or seed species.
  • Respiratory quotient is produced CO₂ divided by consumed O₂. The absorber removes all produced CO₂ in this ideal model; other gases are inert.
  • The manometer reports pressure difference divided by water density and gravity. Its graphical movement is compressed and its liquid displacement does not feed back on chamber volume.
  • This is a virtual comparison, not a practical protocol for using carbon dioxide absorbents.

Try this in class

  1. Q1Why can oxygen be consumed while the pressure signal stays zero?
  2. Q2Why does oxygen consumption slow near exhaustion?

Frequently asked questions

Does a flat manometer prove the seeds are not respiring?

No. At respiratory quotient one without an absorber, produced carbon dioxide exactly replaces consumed oxygen in this ideal pressure balance.

Is the temperature control a measured species response?

No. It applies a stated illustrative Q10 and begins a fresh equilibrated trial.